"Love, having become a god, becomes a demon"

I've really appreciated the perspective that sin is idolatry. Tim Keller, among others, have really done a good job of explaining this. (Keller has a book coming out later this year on the topic.)

C.S. Lewis explains how relationships can become idols:

If Affection is made the ultimate sovereign of a human life the seeds will germinate. Love, having become a god, becomes a demon. (Four Loves, p.56)